Various apparatuses, such as hypodermic syringes and intravenous needles, are utilized for injecting a substance into humans and animals. Apparatuses of this type typically comprise a body adapted to have the substance to be injected passed therethrough and a needle mounted on the body. The substance to be injected can be forced through the needle in various ways, such as by a plunger carried by the body or by external means, such as a pump or gravitational flow.
Apparatuses of this type are typically disposable and are discarded after use. One problem presented by the disposal of these apparatuses is in shielding the sharp end of the needle so that those handling it will not be stuck. This is particularly important because, following the injection, the needle may be contaminated and spread blood-transmitted diseases, such as hepatitis or AIDS.
Our U.S. Pat. No. 4,425,120 discloses a shielded hypodermic syringe in which a guard can be slid along the body from a retracted position to an extended position. In the extended position, the guard covers the point of the needle so as to protect those handling it from being stuck by the needle point. The guard is normally releasably retained in a retracted position. To actuate the guard, the guard is first rotated in one direction to release it, then advanced axially to the extended position and finally rotated to positively lock the guard in the extended position. Although the patented construction is very satisfactory, it is desired to provide for the locking and releasing of the guard without the need to employ rotational movement of the guard.